Department of Fish Ecology and Evolution, Center for Ecology, Evolution and Biogeochemistry, EAWAG, Swiss Federal Institute of Aquatic Science and Technology, Kastanienbaum, Switzerland.
Community Dynamics Group, Department of Evolutionary Ecology, Max Planck Institute for Evolutionary Biology, Plön, Germany.
Mol Ecol. 2024 May;33(10):e16939. doi: 10.1111/mec.16939. Epub 2023 Apr 6.
Host-parasite interactions can cause strong demographic fluctuations accompanied by selective sweeps of resistance/infectivity alleles. Both demographic bottlenecks and frequent sweeps are expected to reduce the amount of segregating genetic variation and therefore might constrain adaptation during co-evolution. Recent studies, however, suggest that the interaction of demographic and selective processes is a key component of co-evolutionary dynamics and may rather positively affect levels of genetic diversity available for adaptation. Here, we provide direct experimental testing of this hypothesis by disentangling the effects of demography, selection and their interaction in an experimental host-parasite system. We grew 12 populations of a unicellular, asexually reproducing algae (Chlorella variabilis) that experienced either growth followed by constant population sizes (three populations), demographic fluctuations (three populations), selection induced by exposure to a virus (three populations), or demographic fluctuations together with virus-induced selection (three populations). After 50 days (~50 generations), we conducted whole-genome sequencing of each algal host population. We observed more genetic diversity in populations that jointly experienced selection and demographic fluctuations than in populations where these processes were experimentally separated. In addition, in those three populations that jointly experienced selection and demographic fluctuations, experimentally measured diversity exceeds expected values of diversity that account for the cultures' population sizes. Our results suggest that eco-evolutionary feedbacks can positively affect genetic diversity and provide the necessary empirical measures to guide further improvements of theoretical models of adaptation during host-parasite co-evolution.
宿主-寄生虫相互作用会导致强烈的种群动态变化，并伴随着抗性/感染性等位基因的选择。人口瓶颈和频繁的选择都预计会减少分离遗传变异的数量，因此可能会限制共进化过程中的适应。然而，最近的研究表明，人口统计学和选择过程的相互作用是共进化动态的一个关键组成部分，并且可能会积极影响适应可用的遗传多样性水平。在这里，我们通过在一个实验性的宿主-寄生虫系统中分离出人口统计学、选择及其相互作用的影响，直接对这一假设进行了实验验证。我们培养了 12 个单细胞、无性繁殖藻类（Chlorella variabilis）种群，这些藻类经历了生长后种群大小保持不变（三个种群）、种群动态变化（三个种群）、暴露于病毒引起的选择（三个种群）或种群动态变化加上病毒引起的选择（三个种群）。在 50 天后（约 50 代），我们对每个藻类宿主种群进行了全基因组测序。我们观察到，在同时经历选择和种群动态变化的种群中，遗传多样性更多，而在这些过程被实验分离的种群中则较少。此外，在那三个同时经历选择和种群动态变化的种群中，实验测量的多样性超过了考虑到培养物种群大小的多样性的预期值。我们的结果表明，生态进化反馈可以积极影响遗传多样性，并提供必要的经验措施，以指导宿主-寄生虫共进化过程中适应理论模型的进一步改进。
